Propeller



' Patented Feb. 2, 1932 UNITED STATES yParleur ori-ica HARRY E. SECMMES, F CHEVY CHASE. MARYLAND, ASSIGNOR T0 AMERICAN PBO- TELLER COMPANY, OF'BALTIMORE, MARYLAND, A CORPORATION OF MARYLAND PROPELLER Application led .Tuly 25,

The invention relates to propellers and more particularly has reference to an airplane propeller which may be effectively used for a great number of flying hours.

s Material employed -in constructing airplane propellers must meet a comparatively i great number of requirements. For example, it must possess suiiicient strength and at the same time be of light weight or low density. Another important property which the material must have is hardness so that it will not pit or fray while it must also be of a nonmoisture absorbent nature.' In addition to the prerequisites just outlined, the propeller material should resist chemical attack, resulting in corrosion and deterioration, while the material should be inexpensive and easily worked.

Up to the present no material possessing all, of these characteristics has been discovered, nor has a combination of materials been employed to construct a propeller which fulfills all of the ideal requirements.

The major object of this invention is to provide an airplane propeller capable of being used fora reat number of flying hours.

An equally important object is to provide an airplane propeller constructed of two different materials.

A further object is to form` a propeller o two dierent materials, one being incased within-the other. A

A further object is to eiectively prevent the failure of a propeller composed of-two materials of diHerent expansion coeilicients,

one material being encased within the other.'

Another object is the provision of apropeller constructed of two materials, one encased within the other, which may be given any desired design.

An additional object is the construction of a propeller formed of a casing of one material and having another material molded therein.

Yet another-object is the provision of a propeller constructed of an impervious material.

Yet another object is the formation of the blade surfaces of a propeller of such material that they will withstand the effects of 1929. serial no. 380,994.

iying in adverse weather and natural conditions.

Still another object is tov provide a propeller having high resistance properties against chemical attack.

A still further object is the provision of va propeller which is simple of design and relatively inexpensive to construct.

With these and other objects in view, which may be incident to my improvements, the invention consists in the parts and combinations to be hereinafter set forth and claimed, with the understanding that the several necessary elements comprising my invention may be varied in construction, pro-. 05 portions and arrangement without departing from the spirit and scope of the appended claims.

The invention comprehends the provision of an airplane propeller of novel design, the construction materials of which are particularly suitable for such a device. One method of successfully effecting the conceptH of this invention is the provision of a metal casing in which is deposited a relatively in- 'fusible organic substance.

In order to make my invention more clearly understood, I have shown, in the accompanying drawings, means for carrying the same into practical efect without limiting 30 the improvements in their useful applications to the particular constructions, which, for the purpose of explanation, have been made the subect of illustration.

In the drawings:

Figure 1 is a plan view of a propeller embodying the 'features of my invention.

Figure 2 is a vertical sectional view showing the blade section along the line 2 2 of Figurel.

Figure 3 is a longitudinal section taken on line 3-3 of Figure 1 and showing the'blade tip`construction.

Figure 4 is a longitudinal section taken along the line 3-3 of Figure 1 and is a con- 953 tinuation of Figure 3.

Shown in Figure 1 is a two bladed propeller having detachable blades 1 and 2 secured in any suitable manner to a hub 3, as, for example, by bolts 4. Provided in the hub is a cylindrical opening 5 having a bushing 6 positioned therein so that the propeller may be mounted upon the driving shaft of a power source.,

As it will be observed in Figure 3, the blades are formed of a casing or cover 7 adapted to encase a filler material 8. Provided in the tip of each blade is a vent 9 adapted to allow air contained within the casing 7 to be forced therethrough while the filler material is being placed within the casing; It is to be understood that the vents 9 are not required to be located at the blade tips, nor are they limited to the number shown, as it is obvious that their location and number may be varied without adecting the spirit of the invention.

Although I have shown a two-bladed propeller of the detachable-blade type, it will hereinafter appear that the invention is not limited to this embodiment, as a propeller possessing any number of blades formed integral with the hub, or an adjustable pitchv propeller is within the concept of my invention. Moreover, I wish it to be understood that the invention is not limited to air screws only, since it is within the scope of my .invention to design a propeller capable of being employed for any use.

The casing 7 is constructed of metal having a relatively thin cross section. Preferably, I

employ stainless steel or materials having similar reslstlve characteristics. yIt is desired to form the filler 8 of a phenolic condensation product. Obviously, however, many types of relatively infusible organic substances may be employed in its place. As an example of this, hard rubber and resinous substances may be used.

A consideration of the properties of the two materials employed in the construction will clearly oint out the advantages to be gained there om.

As it is well-known, formulas for stainless steel have been so successfully developed that all fear of the metal becoming corroded or' rusted has been overcome. At the same time, tests have conclusively proven that phenolic condensation products, of both the laminated and pure resin type, present high resistant powers to chemical attack. Consequently, in this respect, both stainless steel and phenolic condensation products fall within the scope ofan ideal material. I

The moisture-absorbing properties of all metals are negligible, and the same is likewise true of phenolic condensation products. Experimental data obtained from the Bureau of Standards showsthat the pure resin will absorb water from .05% to .07% of its weight. In the Air Service, the average moisture content encountered for wood ranges from 10% to 12%. The superiority of phenolic condensation products over wood is consequently ap- 35 parent. The combination of these two materials will therefore effectively fulfill this requirement of the ideal material. 4

As has been previously ointed out, the most serious defect of Woo en and phenolic material propellers has been that they are subject to a considerable pitting and fraylng action, resulting from flying under adverse conditions. By encasing a phenolic condensation product within a metal cover, this defect is eliminated, as the hardness of stainless steel is more than sufficient to resist such effects.

Preferably, the casing 7 is made up of material having a relatively thin cross section. Despite the fact'that stainless steel possesses a density or unit weight of approximately 0.285 pounds per cubic inch, the thinness of the casing will materially reducet the unit weight of the fully assembled propeller. Counteracting this is the extremely low unit weight of the phenolic resin. Pure phenolic resin possesses a density of 0.0434 to 0.0466 pounds per cubic inch, depending upon the condition of the material. Tests have shown that the density of pure resin is lower than the density of the material formed by impregnating a librous substance with the pure resin.

Consequently, it maybe observed that the advantages of a propeller possessing a low weight are obtained.

Propellers of laminated phenolic material l -pressive strength of from 26,000 to 33,000

pounds per square inch. These are minimum and maximum values for tests which have been made. In considering the minimum values, which would be used in the construction of the air screw, the fact that stainless steel possesses a tensile strength which is over 80,000 pounds per square inch, with a similar compressive strength, must be borne in mind. The strength of the steel will consequently be suflicient to take care of the low tensile strength of the phenolic resin.

In constructing the propeller, a sheet metal casing may be formed by stamping, or a metal blank may be cut out and formed into the desired blade shape. Such a blank would be secured along its ed es by any suitable means as, for example, we ding, riveting or crimping. The construction of hollow metal propeller blades is well-known to the art, and any suitable manner of forming them may be employed in my invention. 4 As has been pointed out in connection with Figure, a vent or opening 9 is shown inthe blade tip.

The blade having been formed 4pure l.

phenolic resin is placed therein by pouring or by any other desired method. The provision of the opening 9 allows the air within the casing to be exhausted and, consequently prevents the formation of voids within the filler. The vents 9`may be sealed after filling the casing with phenolic resin. Having placed the resin Within the casing, the whole blade is subjected to heat and pressure, which causes the fluid phenolic condensation product to harden and to be molded within the metal cover.

The materials employed in constructing the propeller are relativelyinexpensive, and, as may be observed, the methodof'construction requires a small amount of skilledworkmanship with the attendant decrease in expense of the finished product.

lVhile stainless steel and pure' phenolic condensation product possess the properties which will-result in an ideal propeller material, the fact that the expansion coeicients of these two substances are far apart must be coped with. Pure phenolic resin possesses a coefficient of linear expansion whichvaries from .00005 to .00011. This variation in the expansion .coelicient is due to the fact thatthis property is variable for different samples of the pure resin. The lowest figure is the minimum given in the International Critical j Tables published bythe Bureau of Standards,

blade surface is provided with series of rows l0A of expansion joints 11. Each expansion joint 11 is constructed of a friable strip of material formed integral with the casing 7 and flush with the blade surface.

As may be observed in Figure 1, the rows 10 of expansion joints 11 are angularly disposed with respect to the plan center line of the blade; and also toeach other. It should be noted that the rows of expansion joints upon each blade surface are formed in two series, the rows in each series being parallel to each other. It should also be noted that the rows of the two series formed upon a blade surface are staggered with respect to each other. As clearly shown in Figure 1, the rows 10 extend from the leading edge of the propeller to a point substantially near the plan center line and similarly from the trailing edge to a point substantially near the plan center line.

It has been pointed out thatv the expansion joints are provided on both the blade -face and the blade backy of the propeller. Each l series of rows upon the blade back is parallel 10 have been grossly exaggerated, and like` wise the ex ansion of the filler material 8, y

as shown in igure 4. It is desired, in forming the expansion joints 10, that relatively small-size friable strips be constructed. Although, as shown in Figure 1, these strips have a curvilinear outline, it is obvious that any other geometric form, such as a triangle or rectangle may be employed. I also wish it to be distinctly understood that my invention is not limited to the number of rows of expansion joints shown in the drawings, as it is possible to use a greater or lesser number of these. Likewise, the construction is not limited to the number of expansion joints in each row as this number may be varied.

When ai rise in temperature causes a suicient expansion of the phenolic condensation product 8, the expansion joints will function' to prevent the failure of the casing. This isl clearly shown in Figure 4, where the filler appears in its expanded form, with the friable strip broken away from the blade surface. By reason of the smallness of the friable At the same time, because of the manner '95 strips 11, it may be seen that their rupture. will not materially weaken the metal casing.4

in which they are positioned and because of their construction, they will adequately allow for the cubical expansion of the filler material 8. f

Upon contraction of the filler 8, caused by a lower temperature, the strips 11 will of course remain intheir ruptured or extended position. However, since they are relatively small, their resistance to the air, when ruptured, mayv be considered as ne ligible.

iMoreover, after the strips have beenv roken,

they may be hammered down Hush with the blade surfaces-without fear of racturing the phenolic condensation product within -thel CaSIl'lg;

From the foregoing description, it will be obvious ,that I have provided a propeller constructed of material which meets all of the ideal requirements. Consequently, a propeller capable of being eiliciently used for a great number of flying hours and which requires a small amount of inspectionv has been effectively embodied in the construction which I have disclosed. Finally, it will be.

observed that a propeller capable of being embodied in anydesign, and which is of inexpensive construction, has beenpprovided.

While I have shown and described the preferred embodiment of my invention, I wish v it to be understood that I do not confine myself to the precise details of construction herein set forth, by vway of illustration, as it is apparent that many changes and variations may be made therein, by those skilled in the art, without departing from the spirit of the invention, or exceeding the scope of the appended claims.

I claim:

1. A propeller having hollow metal blades filled with a'resinous material.

2. A propeller having blades formed of a phenolic condensation product incased in a metal cover.

3. A propeller having blades formed of a metallic casing and a synthetic resin molded therein.

4. A propeller having blades formed of a metallic casing and a phenolic condensation product molded therein.

5. A propeller having blades formed of a synthetic resin incased in a metallic cover provided with a plurality of expansion joints adapted to allow for the unequal expansion of the two materials.

6. A propeller having blades formed of a phenolic condensation product incased in a metallic cover provided with a plurality of expansion joints adapted to allow for the unequal expansion of the two materials.

7. In a propeller formed of a phenolic conn densation product incased in a metal cover,

an expansion joint provided by a frangible tongue formed integral with the metal cover.

8. In a propeller formed of a phenolic condensation product incased in a metal cover, a fplurality of rows of expansion joints, each o said joints being Vconstructed of a frangible tongue of material formed integral with the metal cover.

9. In a. propeller formed of a phenolic condensation product incased in a metal cover, a plurality of rows of expansion joints, each rowbeing positioned in the cover so that it is angularly disposed with respect to the plan center line of the propeller.

10. In a propeller formed of a phenolic condensation product incased in a metal cover, series of rows of expansion joints posi.- tioned upon the opposite cover surfaces, each row of each series being angularly disposed with respect to the plan center line of the propeller and to any'other row of another series.

11. In a propeller formed of aphenolic condensation product incased in a metal cover, series of rows of expansion 'oints positioned upon the face and back og each propeller blade, the rows of each series upon either blade surface being substantially parallel and staggered with respect to each other.

12. In a propeller formed of a phenolic Y condensation product incased in a. metal cover, a series of rows of expansion joints positioned upon the face of each propeller ade so that each row extends from the leading edge to a point substantially near the center of the blade face, a second series of rows of expansion joints staggered with respect to the first and extending from the trailing edge to a point substantially near the center of the blade face positioned thereon, and series of rows of expansion joints ilmlarly positioned upon the back of each 13. In a propeller formed of a phenolic condensation product incased in a metal cover, a series of staggered rows of expansion joints vpositioned u on the face of'each blade, similar series o rows of expansion joints positioned upon the back of each blade, the rows thereon also being staggered with respect to the rows of expansion joints on the blade face.

14. A propeller having blades formed of a synthetic resin, and a metallic casing therefor encasing said resin at least partially.

In testimony whereof I aix my signature. 

